1. Field of the Invention
The present invention relates to a control device for an occupant protection device, for controlling activation of the occupant protection device such as a seat belt device or an inflatable restraint such as an airbag device that protects an occupant in the event of a vehicle collision. More particularly, the present invention relates to a control device for an occupant protection device which uses output signals of satellite sensors (collision detectors) arranged on a vehicle front side positioned offset from a center position in a vehicle width direction.
2. Description of Related Art
An occupant protection device such as an airbag device or a seat belt device is provided in order to restrain an occupant of a vehicle in the event of a collision. When a vehicle collides with an obstacle, a collision detection sensor outputs a detection signal to a control device to operate the occupant protection device. For example, although the collision detection sensor (a main sensor) is provided in the control device disposed in a central portion (for example, a center floor) of a vehicle, it is desirable to additionally provide a collision sensor (a satellite sensor) for detecting a collision in a crash zone or the like of a vehicle front portion in order to detect a vehicle collision quickly and to restrain an occupant appropriately. For example, Japanese Patent Application Publication No. 2005-306185 discloses a configuration in which one or a plurality of satellite sensors is disposed in a vehicle front portion. Specifically, it is proposed that an occupant protection device be controlled based on an output signal having the highest signal level among the deceleration output signals of a plurality of collision detection sensors (acceleration sensors).
For example, when two satellite sensors are disposed in the vehicle front portion, the satellite sensors are typically disposed at symmetrical positions in relation to a center line in a vehicle width direction (extending in a vehicle front-rear direction). Moreover, when only one satellite sensor is disposed in the vehicle front portion, the satellite sensor is generally disposed on a vehicle center line. When the satellite sensor is disposed on the center line, it is convenient because detection sensitivity characteristics do not vary depending on a collision position on the vehicle front side when detecting a head-on collision (a frontal collision), an offset collision (a vehicle front-right side collision or a vehicle front-left side collision), or other collisions.
However, when only one satellite sensor is disposed in the vehicle front portion, it may not be possible to dispose the satellite sensor on the vehicle center line due to vehicle design conditions. In this case, the problems described below may occur.
For example, when a satellite sensor is disposed closer to the left side than the vehicle center line, the satellite sensor outputs a high-level detection signal in the event of a vehicle front-left side collision (because the satellite sensor is disposed relatively close to the collision position) even if the collision speed is the same for a center mounted sensor. Moreover, the offset satellite sensor outputs a low-level detection signal in the event of a vehicle front-right side collision (because the satellite sensor is disposed relatively distant from the collision position). From the detection signal of the satellite sensor, it is difficult to distinguish between a vehicle front-left side collision with a relatively low collision speed and a vehicle front-right side collision with a relatively high collision speed. The same problem occurs when the satellite sensor is disposed closer to the right side than the vehicle center line.
For example, one satellite sensor may be disposed on the left side of the vehicle center line and one satellite sensor for compensation of detection characteristics may be disposed on the right side of the vehicle center line. In this case, for example, the detection sensitivity can be compensated for by calculating an average value of the output values of the two satellite sensors or by selecting the higher value of the output values. However, such a detection sensitivity compensation method cannot be employed when only one satellite sensor is used.